Radio network node, wireless device, and methods for performed in a wireless communication network

ABSTRACT

Embodiments herein relate, for example, to operations performed by a network node for handling communication of a wireless device in a wireless communication network. The network node receives a first preamble associated with a first downlink (“DL”) beam from the wireless device. The network node transmits a random access response (“RAR”) to the wireless device using the first DL beam associated with the first preamble. Responsive to transmitting the RAR using the first DL beam, the network node determines that the wireless device has not received the RAR. Responsive to determining that the wireless device has not received the RAR, the network node transmits the RAR using a second DL beam.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/605560 filed Oct. 16, 2019, which is a 35 U.S.C. § 371 national stageapplication of PCT International Application No. PCT/SE2018/050491 filedon May 14, 2018, which in turns claims domestic priority to U.S.Provisional Patent Application No. 62/505,145, filed on May 12, 2017,the disclosures and content of which are incorporated by referenceherein in their entirety.

TECHNICAL FIELD

Embodiments herein relate to a radio network node, a wireless device andmethods performed therein regarding wireless communication. Furthermore,a computer program product and a computer-readable storage medium arealso provided herein. In particular, embodiments herein relate tohandling communication of the wireless device in a wirelesscommunication network.

BACKGROUND

In a typical wireless communication network, wireless devices, alsoknown as wireless communication devices, mobile stations, stations (STA)and/or user equipments (UE), communicate via a Radio access Network(RAN) to one or more core networks (CN). The RAN covers a geographicalarea which is divided into service areas or cell areas, with eachservice area or cell area being served by a radio network node such asan access node e.g. a Wi-Fi access point or a radio base station (RBS),which in some networks may also be called, for example, a NodeB, aeNodeB, or gNodeB. The service area or cell area is a geographical areawhere radio coverage is provided by the radio network node. The radionetwork node operates on radio frequencies to communicate over an airinterface with the wireless devices within range of the radio networknode. The radio network node communicates over a downlink (DL) to thewireless device and the wireless device communicates over an uplink (UL)to the radio network node.

A Universal Mobile Telecommunications System (UMTS) is a thirdgeneration telecommunication network, which evolved from the secondgeneration (2G) Global System for Mobile Communications (GSM). The UMTSterrestrial radio access network (UTRAN) is essentially a RAN usingwideband code division multiple access (WCDMA) and/or High-Speed PacketAccess (HSPA) for communication with user equipments. In a forum knownas the Third Generation Partnership Project (3GPP), telecommunicationssuppliers propose and agree upon standards for present and futuregeneration networks and UTRAN specifically, and investigate enhanceddata rate and radio capacity. In some RANs, e.g. as in UMTS, severalradio network nodes may be connected, e.g., by landlines or microwave,to a controller node, such as a radio network controller (RNC) or a basestation controller (BSC), which supervises and coordinates variousactivities of the plural radio network nodes connected thereto. The RNCsare typically connected to one or more core networks.

Specifications for the Evolved Packet System (EPS) have been completedwithin the 3^(rd) Generation Partnership Project (3GPP) and this workcontinues in the coming 3GPP releases, such as 4G and 5G networks. TheEPS comprises the Evolved Universal Terrestrial Radio Access Network(E-UTRAN), also known as the Long-Term Evolution (LTE) radio accessnetwork, and the Evolved Packet Core (EPC), also known as SystemArchitecture Evolution (SAE) core network. E-UTRAN/LTE is a 3GPP radioaccess technology wherein the radio network nodes are directly connectedto the EPC core network. As such, the Radio Access Network (RAN) of anEPS has an essentially “flat” architecture comprising radio networknodes connected directly to one or more core networks.

With the emerging 5G technologies such as New Radio (NR), the use ofvery many transmit- and receive-antenna elements is of great interest asit makes it possible to utilize beamforming, such as transmit-side andreceive-side beamforming. Transmit-side beamforming means that thetransmitter can amplify the transmitted signals in a selected directionor directions, while suppressing the transmitted signals in otherdirections. Similarly, on the receive-side, a receiver can amplifysignals from a selected direction or directions, while suppressingunwanted signals from other directions.

Beamforming allows the signal to be stronger for an individualconnection. On the transmit-side this may be achieved by a concentrationof the transmitted power in the desired direction(s), and on thereceive-side this may be achieved by an increased receiver sensitivityin the desired direction(s). This beamforming enhances throughput andcoverage of the connection. It also allows reducing the interferencefrom unwanted signals, thereby enabling several simultaneoustransmissions over multiple individual connections using the sameresources in the time-frequency grid, so-called multi-user MultipleInput Multiple Output (MIMO).

In LTE, a connected wireless device is configured to perform RadioResource Management (RRM) measurements and report them based on eventsthat can be triggered. Network is assisted by these reports to takedecisions whether the connection should be moved from one cell toanother. If a decision is made, the radio network node sends a handovercommand to the wireless device, i.e. an RRCConnectionReconfigurationmessage with the mobilityControlInformation IE which contains, amongother information, the necessary information to access the target cell,such as the Random Access Channel (RACH) configuration, i.e. time andfrequency resources for the Physical Random Access Channel (PRACH) andpossibly a dedicated random access preamble.

In NR, it has been agreed that the same principles should follow i.e.the handover should contain all the necessary information that enablesthe wireless device to access the target cell. In other words, thewireless device also needs to have the RACH configuration, i.e. time andfrequency resources for the PRACH and possibly a dedicated preamble.However, differently from LTE, the random access procedure and PRACH inNR will have a design that enables the network to:

-   -   Use analog beamforming at the Reception (RX) side to improve the        PRACH detection;    -   By the preamble detection the radio network node is able to know        the best DL beam to at least transmit a random access response        (RAR).

As a consequence of these, the random access procedures in NR can beassumed to have the following characteristics:

-   -   The wireless device should be able to detect a DL beam in the        cell the wireless device should access, either during a        handover, in which case the accessed cell is a target cell, or        initial access, in which case the accessed cell is the cell the        wireless device is camping on;    -   To enable analog RX beamforming when receiving the random access        preamble, on the PRACH, in the radio network node such as the        gNB, there should be a mapping between that DL beam, or groups        of DL beams, and the RACH configuration, i.e. time/frequency        resources and optionally preamble subset, so analog beamforming        can listen in the correct directions in the right time to        receive UL transmissions on the PRACH.

In NR, there is currently a discussion for the specific structure of thesynchronization signals (SS) and reference signals (RS) to supportprocedures such as random access, which is necessary during handoversand transitions from idle to connected state. It is herein described howa wireless device would access a target cell in RRC_CONNECTED state inNR under current assumptions/agreements in the TSG-RAN Working Group 1(RAN1) and TSG-RAN Working Group 2 (RAN2) in 3GPP.

A combination of NR synchronization sequences e.g. NR-PrimarySynchronization Signal (PSS)/Secondary Synchronization Signal (SSS), andPhysical Broadcast Channel (PBCH) may constitute a so called SS Block.That may also contain a Tertiary Sync Signal (TSS) to indicate theOrthogonal Frequency-Division Multiplexing (OFDM) symbol timing orequivalent information, but the TSS is still For Further Study (FFS) inWG RAN1. An RRC_CONNECTED wireless device trying to access a target cellmay assume that the SS Block may be transmitted in the form ofrepetitive bursts of SS Block transmissions, denoted “SS Burst”, whereinsuch a SS burst consists of a number of SS Block transmissions followingclose, i.e. within a timer interval, after each other in time.Furthermore, a set of SS Bursts may be grouped together, denoted “SSBurst Set”, where the SS Bursts in the SS Burst Sets are assumed to havesome relation to each other, e.g. that the SS Block transmissions in theSS Burst Set together forms a complete beam sweep, covering the entireintended coverage area. Both SS Bursts and SS Burst Sets have theirrespective given periodicity. In the single beam scenarios, the networkcould configure time-repetition within one SS Burst in a wide beam. Inmulti-beam scenarios, at least some of these signals and physicalchannels, e.g. SS Block, may be transmitted in multiple beams, whichcould be done in different manners depending on network implementation,as shown in FIG. 1.

FIG. 1 shows examples of different configurations of an SS Burst Set.Top: Time-repetition within one SS Burst in a wide beam. Middle:Beam-sweeping of a small number of beams using only one SS Burst in theSS Burst Set. Bottom: Beam-sweeping of a larger number of beams usingmore than one SS Burst in the SS Burst Set to form a complete sweep. Toimplement which of these three alternatives is a network vendor choice.That choice depends on the tradeoff between i) the overhead caused bytransmitting periodic and always on narrow beam sweepings vs. ii) thedelays and signaling needed to configure the wireless device to find anarrow beam for Physical Downlink Shared Channel (PDSCH) and PhysicalDownlink Control Channel (PDCCH). The implementation shown in the upperfigure prioritizes i), while the implementation shown in the bottomfigure prioritizes ii). The figure in the middle case is an intermediatecase, where a sweeping of wide beams is used. In that case the number ofbeams to cover the cell is reduced, but in some cases an additionalrefinement is needed for narrow gain beamforming of PDSCH.

Let us now assume the different beamforming implementations for the SSBlock transmissions in the case of handovers and assume that the targetcell implements one of these alternatives.

In the case on top, where a single beam transmits the SS Burst Set, thehandover command contains a single RACH configuration for the targetcell. Once the wireless device receives the handover command it willaccess the target and a random access procedure will be triggered by thewireless device sending a random access preamble. Unless directionalreciprocity is assumed in the radio network node, such as a Transmissionand Reception Point (TRP) or gNB, receiving the preamble, the targetcell will transmit the random access response (RAR) either by sweepingbeams in all directions until the wireless device detects and transmitsa handover (HO) complete message, or something equivalent to notify thatthe handover has been completed at the wireless device, or transmittingthe RAR with time repetition in a wider beam and expect the HO completemessage. In any of these cases, after the handover, depending on thedata rates/service, the desired wireless device performance requiresthat the target cell triggers a beam management operation of beamrefinement, enabling the wireless device to use a narrow beam for PDCCHand PDSCH in the target cell. That may require an additionalconfiguration, using Radio Resource Control (RRC) and/or Layer one andLayer two (L1/L2) signaling, additional measurement and reportingmechanisms and additional delay to perform measurements in the targetcell e.g. based on Channel State Information-Reference Signal (CSI-RS)processes configured for beam management. In other words, after thehandover, it may take some time until the wireless device again canaccess a narrow beam in the target cell, so it may take some time untilthe target cell can start to beamform PDSCH with high gain enabling highdata rates.

In the bottom case, where multiple narrow beams are used to transmit theSS Burst Set, the handover command may contain multiple RACHconfigurations for the target cell, possibly associated with the SSBlock beams or groups of SS Block beams from target cell. Once thewireless device receives the handover command it will select a beam inthe target cell, check how it maps to the received RACH configurationper beam and initiate a random access procedure by sending a randomaccess preamble associated with a target cell, beam or a group of beams,using the PRACH resources associated with the target cell, beam or groupof beams. A possible mapping is shown in FIG. 2. FIG. 2 shows an examplewhere each SS Block contains a mapping between RACH configuration andthe strongest DL beam transmitting the SS Block. In this example, eachPRACH occasion or resource is associated with two SS Block beams. Evenwithout directional reciprocity in the radio network node, theimplementation enables the target cell to transmit the RAR in thestrongest DL beam covering the wireless device thanks to the mappingbetween RACH configuration (including the preamble) and the target cellDL beam. That allows the wireless device to quickly access a narrow beamin the target right after handover execution. Despite its benefit, sucha solution has disadvantages in the form of rather high overhead andaccess latency, especially considering the following facts:

-   -   1) Most of the time when the sweeping of narrow beams of the SS        Burst is being used, handovers are not even occurring. Hence,        using the solution to enable a quick access to narrow beams in a        target cell may be too costly without clear benefits in some        cases.    -   2) In many cases, handovers would not really require an incoming        wireless device to rely on a narrow gain beam in the target. In        some cases, when the wireless device uses a low data rate        service or is not even continuously transmitting data and then a        wide beam access in the target could be sufficient. Hence, the        overhead would not be needed in some handovers.

The middle case, where beam sweeping is considered but wide beams areused to reduce the overhead, is an attempt to find a compromise betweenoverhead and quick access to a beam. However, the solution does also notconsider the previously described facts 1) and 2) since it is a staticconfiguration. In other words, although the solution tries to enable thewireless device to access a DL beam at the target after handoverexecution, in some cases where the wireless device requires a refined DLbeam, additional steps will anyway be needed in the target for beamrefinement.

In summary, defining as narrow beams as possible in the SS Burst Set, asshown at the bottom of FIG. 1, speeds up the wireless device access to avery narrow beam. On the other hand, the cost for that is thetransmission of periodic beam sweepings of the SS Blocks in narrowbeams, which may represent a significant overhead considering that itmight mainly be useful these periods when the network, e.g. aneighboring gNB considers a handover into the cell for a wirelessdevice. During initial access, one could claim that data connectivityhas not yet started, hence, the wireless device may afford to start witha wide DL beam transmission until the network configures a set of CSI-RSprocesses for beam refinement i.e. selection within the wide beam forhigher data rates. However, in the case of handovers, a wireless devicemight already have a high data rate service in the serving cell so thata handover to a wide beam and then perform beam refinement may representa non-seamless handover at least for some services.

FIG. 1 shows an example of a handover execution followed by beamrefinement. That step of beam refinement may anyway be necessary in thecase of wide beam sweeping transmissions or repetition of the SS Block.Handing over to a target cell may fail when using beamforming leading toa reduced or limited performance of the wireless communication network.

SUMMARY

An object of embodiments herein is to provide a mechanism that improvesperformance of the wireless communication network when handlingcommunication, e.g. handling handover of a wireless device, for wirelessdevices in a wireless communication network.

According to an aspect the object is achieved by providing a methodperformed by a wireless device for handling communication in a wirelesscommunication network. The wireless device transmits to a radio networknode, a first preamble associated with a selected DL beam. The wirelessdevice further monitors for a RAR in a first RAR reception window andwhen the RAR is not received in the first RAR reception window, thewireless device monitors for the RAR in a second RAR reception window ofa different beam; or the wireless device transmits, to the radio networknode, a second preamble associated with a second beam wherein the firstpreamble is associated with a channel state information reference signaland the second preamble is associated with a synchronization signalblock.

According to another aspect the object is achieved by providing a methodperformed by a radio network node for handling communication of awireless device in a wireless communication network. The radio networknode receives a first preamble associated with a DL beam, e.g. apreamble mapped to a certain beam. The radio network node furthertransmits a RAR using the DL beam associated with the first preamble.The radio network node further detects whether the wireless device hassuccessfully received the RAR or not. The radio network node furthersends the RAR a second time using a different beam when detected thatthe wireless device 10 has not successfully received the RAR, whereinthe different beam covers the DL beam the wireless device has initiallyselected.

It is furthermore provided herein a computer program product comprisinginstructions, which, when executed on at least one processor, cause theat least one processor to carry out any of the methods above, asperformed by the wireless device or the radio network node. It isadditionally provided herein a computer-readable storage medium, havingstored thereon a computer program product comprising instructions which,when executed on at least one processor, cause the at least oneprocessor to carry out the method according to any of the methods above,as performed by the wireless device or the radio network node.

According to yet another aspect the object is achieved by providing awireless device for handling communication in a wireless communicationnetwork. The wireless device is configured to transmit, to a radionetwork node, a first preamble associated with a selected downlink beam.The wireless device is further configured to monitor for a RAR in afirst RAR reception window; and when the RAR is not received in thefirst RAR reception window, the wireless device is configured to monitorfor the RAR in a second RAR reception window of a different beam; or totransmit, to the radio network node, a second preamble associated with asecond beam wherein the first preamble is associated with a channelstate information reference signal and the second preamble is associatedwith a synchronization signal block.

According to still another aspect the object is achieved by providing aradio network node for handling communication of a wireless device in awireless communication network. The radio network node is configured toreceive a first preamble associated with a DL beam and transmit a RARusing the DL beam associated with the first preamble. The radio networknode is further configured to detect whether the wireless device hassuccessfully received the RAR or not; and to send the RAR a second timeusing a different beam when detected that the wireless device has notsuccessfully received the RAR, wherein the different beam covers the DLbeam the wireless device has initially selected.

According to yet another aspect the object is achieved by providing awireless device comprising processing circuitry configured to transmit,to a radio network node, a first preamble associated with a selecteddownlink beam. The processing circuitry is further configured to monitorfor a RAR in a first RAR reception window; and when the RAR is notreceived in the first RAR reception window, the processing circuitry isconfigured to monitor for the RAR in a second RAR reception window of adifferent beam; or to transmit, to the radio network node, a secondpreamble associated with a second beam wherein the first preamble isassociated with a channel state information reference signal and thesecond preamble is associated with a synchronization signal block.

According to still another aspect the object is achieved by providing aradio network node comprising processing circuitry configured to receivea first preamble associated with a DL beam and transmit a RAR using theDL beam associated with the first preamble. The processing circuitry isfurther configured to detect whether the wireless device hassuccessfully received the RAR or not; and to send the RAR a second timeusing a different beam when detected that the wireless device has notsuccessfully received the RAR, wherein the different beam covers the DLbeam the wireless device has initially selected.

The solution enables the wireless device and network to identifypotential error cases when a beam selection, e.g. narrow beam selection,is performed combined with a handover (and/or a transition from inactiveto connected state based on a narrow DL beam and/or addition of aconnectivity leg to establish dual connectivity or multi-connectivity orto add a component carrier for carrier aggregation) and perform fallbackto the second beam, such as a wide beam, when some kind of failure inthe RAR reception is detected. One advantage is that one can use e.g.wide beams for static signals, use narrow beams for dynamic beamformingand, in the case of failures caused by the narrow DL beam, the networkand the wireless device can fall back to the usage of wide beams. Notethat the narrow beams used for transmission of additional RS may betemporarily transmitted, i.e. beam swept and/or repeated during alimited time period, and during this limited time period they may betransmitted with shorter intervals between the transmissions (even backto back) than the intervals being used for the static signals. Thus,since the fallback of using the second beam, e.g. wide beam, allows thecommunication to continue during the handover the performance of thewireless communication network is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described in more detail in relation to theenclosed drawings, in which:

FIG. 1 is a schematic overview depicting examples of differentconfigurations of an SS Burst Set;

FIG. 2 is a schematic overview depicting mapping of a SS block to aPRACH;

FIG. 3 is a schematic overview depicting a beam refinement procedure;

FIG. 4 is a schematic diagram depicting a wireless communicationsnetwork according to embodiments herein;

FIG. 5a shows configurations of subframes for beam transmissions;

FIG. 5b shows a signaling flow diagram where the optimized handoverexecution is combined with beam selection process;

FIG. 6a shows PRACH multiplexing with PUSCH and PUCCH;

FIG. 6b shows Timing of the Random Access Response window;

FIG. 7a is a flowchart depicting a method performed by a wireless deviceaccording to embodiments herein;

FIG. 7b is a flowchart depicting a method performed by a network nodesuch as a location server according to embodiments herein;

FIG. 7c is a combined flowchart and signalling scheme according toembodiments herein;

FIG. 8 is a combined flowchart and signalling scheme according toembodiments herein;

FIG. 9 shows an example of a method performed by a network nodeaccording to embodiments herein;

FIG. 10 is a schematic block diagram depicting a network node accordingto embodiments herein;

FIG. 11 is a schematic block diagram depicting a wireless deviceaccording to embodiments herein;

FIG. 12 schematically illustrates a telecommunication network connectedvia an intermediate network to a host computer;

FIG. 13 is a generalized block diagram of a host computer communicatingvia a base station with a user equipment over a partially wirelessconnection; and

FIGS. 14-17 are flowcharts illustrating methods implemented in acommunication system including a host computer, a base station and auser equipment.

DETAILED DESCRIPTION

Embodiments herein relate to wireless communication networks in general.FIG. 4 is a schematic overview depicting a wireless communicationnetwork 1. The wireless communication network 1 comprises one or moreRANs and one or more CNs. The wireless communication network 1 may useone or a number of different technologies, such as Wi-Fi, Long TermEvolution (LTE), LTE-Advanced, Fifth Generation (5G), Wideband CodeDivision Multiple Access (WCDMA), Global System for Mobilecommunications/enhanced Data rate for GSM Evolution (GSM/EDGE),Worldwide Interoperability for Microwave Access (WiMax), or Ultra MobileBroadband (UMB), just to mention a few possible implementations.Embodiments herein relate to recent technology trends that are ofparticular interest in a 5G context, however, embodiments are alsoapplicable in further development of the existing wireless communicationsystems such as e.g. WCDMA and LTE.

In the wireless communication network 1, a wireless device e.g. awireless device 10 such as a mobile station, a non-access point (non-AP)STA, a STA, a user equipment and/or a wireless terminal, may communicatevia one or more Access Networks (AN), e.g. RAN, to one or more corenetworks (CN). It should be understood by the skilled in the art that“wireless device” is a non-limiting term which means any terminal,wireless communication terminal, user equipment, Machine TypeCommunication (MTC) device, Device to Device (D2D) terminal, or nodee.g. smart phone, laptop, mobile phone, sensor, relay, mobile tablets oreven a small base station capable of communicating using radiocommunication with a network node within an area served by the networknode.

The wireless communication network 1 comprises a first radio networknode 12 providing radio coverage over a geographical area, a firstservice area 11, of a first radio access technology (RAT), such as NR,LTE, Wi-Fi, WiMAX or similar. The first radio network node 12 may be atransmission and reception point, a Wireless Local Area Network (WLAN)access point or an Access Point Station (AP STA), an access node, anaccess controller, a base station, e.g. a radio base station such as aNodeB, an evolved Node B (eNB, eNode B), a gNodeB, a base transceiverstation, a radio remote unit, an Access Point Base Station, a basestation router, a transmission arrangement of a radio base station, astand-alone access point or any other network unit or node capable ofcommunicating with a wireless device within the area served by the firstnetwork node 12 depending e.g. on the first radio access technology andterminology used. The first radio network node 12 may alternatively oradditionally be a controller node or a packet processing node such as aradio controller node or similar. The first network node may be referredto as a serving network node wherein the first cell may be referred toas a serving cell, and the serving network node communicates with thewireless device 10 in form of DL transmissions to the wireless device 10and UL transmissions from the wireless device 10.

The wireless communication network 1 further comprises a second radionetwork node 13, also referred to as the radio network node, providingradio coverage over a geographical area, a second service area 14, of asecond radio access technology (RAT), such as NR, LTE, Wi-Fi, WiMAX orsimilar. The second radio network node 13 may be a transmission andreception point, a Wireless Local Area Network (WLAN) access point or anAccess Point Station (AP STA), an access node, an access controller, abase station, e.g. a radio base station such as a NodeB, an evolved NodeB (eNB, eNode B), a gNodeB, a base transceiver station, a radio remoteunit, an Access Point Base Station, a base station router, atransmission arrangement of a radio base station, a stand-alone accesspoint or any other network unit or node capable of communicating with awireless device within the area served by the second radio network node13 depending e.g. on the first radio access technology and terminologyused. The second radio network node 13 may alternatively or additionallybe a controller node or a packet processing node such as a radiocontroller node or similar. The second radio network node 13 may bereferred to as a neighbouring network node wherein the second servicearea may be referred to as a neighbouring cell, and the second radionetwork node 13 communicates with the wireless device 10 in form of DLtransmissions to the wireless device 10 and UL transmissions from thewireless device 10.

It should be noted that a service area may be denoted as cell, beam,beam group or similar to define an area of radio coverage. The first andsecond RAT may be the same RAT. Furthermore each cell is exemplified asbeing provided by separate radio network nodes but may in fact beprovided by a same radio network node such as the first or the secondradio network node. Thus, the first or second radio network node mayprovide multiple cells or radio coverage areas.

The radio network nodes transmit RSs, such as CSI-RSs over respectiveservice area. Hence, the first and second radio network nodes transmitMRS, CSI-RSs or beam reference signals (BRS), repeatedly, in time, in alarge number of different directions using as many Tx-beams as deemednecessary to cover an operational area of the respective radio networknode. Hence the first radio network node 12 provides radio coverage overthe first service area using a first reference signal, e.g. first MRS,for identifying the first service area 11 in the wireless communicationnetwork. The second radio network node 13 provides radio coverage overthe second service area 14 using a second reference signal, e.g. secondMRS, for identifying the second service area 14 in the wirelesscommunication network. These reference signals, first and second MRS,may be initiated upon request from a radio network node, e.g. aneighboring radio network node, or configured to be sent continuously.

The problem described herein, i.e. reduced performance upon changingcell, may be solved by a method where inter-cell mobility, i.e. movementbetween different cells, and narrow DL beam selection are jointlyperformed. That is done with the help of an additional RS transmitted innarrow DL beams, compared to the beams transmitting in the SS BlockBurst Sets, where the additional RS may be a configured CSI-RSassociated with the target cell associated with the handover execution.

The network may provide to the wireless device 10, such as anRRC_CONNECTED wireless device, a mapping between RACH configurations andreference signals (RS) that can be transmitted with high gainbeamforming, which are different than reference signals of staticsignals transmitted in wide beams. Static signals may be the ones in NRtransmitted in the SS Block, such as NR-PSS/NR-SSS/TSS and demodulationreference signal (DMRS) for PBCH, while the additional RS may be aCSI-RS. At the network side, the additional RS may be transmitted innarrow beams while beamforming the SS Block transmissions in wide beams.The RS-RACH configuration mapping may be provided when the networkdecides to handover the wireless device from a serving cell to a targetcell and/or when the network wants to establish a dual connectivity, amulti-connectivity, a carrier aggregation or equivalent. This may be thecase when the wireless device is connected to LTE and an NR cell is atarget cell candidate or a potential secondary cell for inter-RAThandover, NR-LTE dual connectivity/tight interworking. Hence, themapping can be provided to the UE in an RRCConnectionReconfigurationmessage associated with a target cell (or candidate to be the SCell) inthe same RAT, denoted as intra-RAT, or in a different RAT, denoted asinter-RAT.

A next step is the DL beam selection at the wireless device during thehandover execution. Therein, the provided mapping may be used during theaccess of a target and/or secondary cell i.e. during a handoverexecution or the establishment/addition of a secondary cell. Afterreceiving the RRC message from the serving cell that triggers the accessto the target or secondary cell, e.g. RRCConnectionReconfiguration, thewireless device then searches for the additional RSs associated with thetarget cell, performs measurements and selects the RS associated withthe best quality, for example, based on best Reference Signal ReceivedPower (RSRP), Signal to Noise plus Interference Ratio (SNIR), signal tonoise ratio (SNR) or some other measure of the signal strength or signalquality. In other words, the wireless device selects the strongest orbest-quality DL narrow beam transmitting the additional RS.

After the selection of the strongest DL beam e.g. based on measurementsof the additional RS, the wireless device 10 initiates a random accessprocedure associated with the configured RACH for the selected RS e.g.uses a RACH preamble or RACH resource mapped to the selected beam.

And, then, DL beam selection at the radio network node for RAR and/orcontrol plane or user plane data starts. Upon the reception of the RACHpreamble in the time and/or frequency resource that maps to a given DLbeam, the network detects what is the strongest DL narrow beam coveringthe wireless device. The radio network node has the option to transmitthe RAR via the detected narrow beam and, even before setting up thebeam management procedure start using the selected DL beam with narrowgain beamforming for data transmission on PDSCH, immediately after thehandover complete message and/or the setup of the secondary cell.

FIGS. 5a and 5b show an example of a configured subframe in the targetcell the wireless device 10 may try to use to select the strongest beamvia CSI-RS measurement between SS Block Bursts and a signaling flowdiagram where the optimized handover execution combined with beamselection is described.

After sending the RACH preamble associated with the selected beam theprior art method assumes that the network maps the detected RACHpreamble and maps to the correct DL narrow beam to transmit the RAR andsubsequently the User Plane (UP) data.

However, different error cases associated with the RACH procedure basedon an additional RS, e.g. CSI-RS in NR, may occur, especially in thecase the wireless device 10 uses as a DL reference signal transmitted ina narrow beam where coverage can be spottier. To understand better theerror cases, one needs to understand the RAR reception in LTE.

Hereinafter the terms time window, window, RAR time window, receptionwindow, RAR reception window, and reception time window may be usedinterchangeably.

At least in LTE, the Random Access Response (RAR) is sent by the secondradio network node 13 on the Physical Downlink Shared CHannel (PDSCH),and addressed with an identity (ID) such as a Random Access RadioNetwork Temporary Identifier (RA-RNTI), identifying a time-frequencyslot in which a preamble was detected. The wireless device 10 expects toreceive the RAR within a time window, of which the start and end areconfigured by e.g. the first radio network node. The earliest subframeallowed by the specifications occurs 2 ms after the end of the preamblesubframe, as illustrated in FIG. 6b . However, a typical delay, e.g.measured from the end of the preamble subframe to the beginning of thefirst subframe of RAR window, is more likely to be 4 ms. The FIGS. 6aand 6b show the RAR consisting of the step 2 message, on PDSCH, togetherwith its downlink transmission resource allocation message ‘G’, on thePhysical Downlink Control Channel (PDCCH). FIG. 6a shows PRACHmultiplexing with PUSCH and PUCCH. FIG. 6b shows Timing of the RandomAccess Response window.

In LTE, at least during initial access, different problems may exist:

-   -   Error case 1: The wireless device 10 does not receive the RAR        within the configured time window;    -   Error case 2: The wireless device 10 receives the PDCCH        signaling indicating the downlink resource used for the RAR but        cannot satisfactorily decode the RAR message.

If the wireless device 10 does not receive a RAR within the configuredtime window, the wireless device 10 may select a preamble again andtransmits another preamble. The minimum delay for the transmission ofanother preamble after the end of the RAR window is 3 ms. If thewireless device receives the PDCCH signaling indicating the downlinkresource used for the RAR but cannot satisfactorily decode the RARmessage itself, the minimum delay is increased to 4 ms, to allow for thetime taken by the wireless device in attempting to decode the RAR. Thefirst radio network node 12 may configure preamble power ramping so thatthe transmission power for each transmitted preamble is increased by afixed step.

A problem in general with handover in NR, which is associated with beammanagement is that after the handover, depending on the data rates orservice, the desired wireless device performance requires that thetarget cell triggers a beam management operation of beam refinement,enabling the wireless device 10 to use a narrow beam for PDCCH and/orPDSCH in the target cell. That may require an additional configuration,e.g. using RRC and/or L1/L2 signaling, additional measurement andreporting mechanisms and additional delay to perform measurements in thetarget cell e.g. based on CSI-RS processes configured for beammanagement. In other words, after the handover, it may take some timeuntil the wireless device 10 again can access a narrow beam in thetarget cell, so it can take some time until the target cell can start tobeamform PDSCH with high gain enabling high data rates. As a result, ifthe wireless device 10 was using high data rate communication usingnarrow, high-gain beamforming in the previous cell, there will be a dipor gap in the data rate—and thus the service quality—in conjunction withthe handover before equally high data rates and service quality can beachieved with a refined beam in the new cell.

A handover procedure may be more sensitive to sudden changes in theradio environment, i.e. the radio channel quality, since a narrow DLbeam is used by the wireless device 10 as DL reference for the PRACHresources, such a time/frequency resource(s), and also which RACHpreamble the wireless device 10 should transmit may be defined. Thenetwork is intended to detect that specific preamble and transmit theRAR in that narrow DL beam corresponding to the detected preamble.

However, one problem that may occur is that a wireless device does notdetect the RAR within the time it has been configured to. In NR that mayoccur if the wireless device selects the wrong DL beam transmitting theadditional RS such as a CSI-RS, or measurements at the wireless deviceabout best beam are outdated so that the wireless device is no longerlocated in the coverage of the beam that was the best during the RSmeasurement procedure. The latter may have two consequences, i.e. twodifferent error cases: 1) the wireless device's shift to a new locationwhen transmitting the preamble may cause the radio network node to failto receive it, because it uses an RX beam (supposedly using analog RXbeamforming) which does not cover the direction in which the preambletransmission from the wireless device arrives; or 2) the radio networknode successfully receives the preamble from the wireless device, e.g.because it uses a wide enough RX beam or because it uses digital RXbeamforming, trying different beamforms using post-processing of thereceived signal, but then the wireless device fails to receive the RAR,because the DL beam the radio network node chooses for the RAR, i.e. theone mapping to the RACH configuration such as UL transmission resourcesand/or preamble, does not reach the wireless device with sufficientlyhigh SINR/SNR.

These are thus additional problems that stem from the use of beamformingin NR, especially when narrow beams are used.

According to embodiments herein the wireless device 10 may be configuredto access a target cell, for example during a handover executionprocedure or during a transition from RRC_INACTIVE to RRC_CONNECTEDstate, with two mappings between DL beams and per cell RACH resources:i) a narrow beam RACH mapping to be initially used to access the targetcell so that target can directly know the best DL narrow beam with whichto send the RAR to the wireless device 10 and start subsequent datatransmission and ii) a wide beam RACH mapping (fallback), to be used inthe case the wireless device 10 and network detects that the firstprocedure has failed.

The wireless device 10 transmits a preamble, a first preamble, inaccordance with a RACH configuration associated with a selected DL beamsuch as a (best) narrow CSI-RS DL beam also referred to as a first beam.

The wireless device 10 then monitors for a RAR in a first RAR receptionwindow e.g. a regular (configured) RAR reception window, in which e.g.the second radio network node 13, in case of successful reception of thefirst preamble, will use narrow beamforming to transmit the RAR. If theRAR is received, none of the herein considered error cases has occurredand the wireless device 10 proceeds with the network access procedure.

However, if the wireless device 10 does not receive any RAR in the firstRAR reception window, it instead transmits a second preamble associatedwith a second beam e.g. a wide beam wherein the first preamble isassociated with channel state information reference signal, i.e. narrowbeam, and the second preamble associated with a synchronization signalblock, i.e. wide beam. Alternatively, the wireless device waits for aRAR in a second reception window, in which the second radio network node13, in case of failure to receive a subsequent, i.e. a messagetransmitted by the wireless device 10 after receiving the RAR, transmitsa RAR using a second e.g. wide(r) beam. Note that this second receptionwindow may also be realized as an extension of the first RAR receptionwindow, essentially forming a single RAR reception window but withextended length. If the wireless device 10 successfully receives a RARin the second (or extended part of the) reception window, the wirelessdevice 10 proceeds with the network access procedure.

However, if the wireless device 10 does not receive any RAR in thesecond (or extended part of the) RAR reception window, the wirelessdevice 10 may transmit the second preamble, this time associated withe.g. a wide beam i.e. a different beam than the selected DL beam. Whendoing this, the wireless device 10 may use the RACH configurationassociated with a wide beam which either has been detected (andselected) previously, e.g. a wide beam SS Block transmission which thewireless device 10 detected when it acquired synchronization in thecell, or which the wireless device 10 identifies during a new wide beamselection procedure. These two alternatives may also complement eachother, such that a second RACH preamble may be transmitted based on theRACH configuration associated with a previously detected, and selected,wide beam, but if no RAR is received in response, then the wirelessdevice 10 performs a new wide beam selection and transmits a thirdpreamble in accordance with the RACH configuration of the newly selectedwide beam.

Optionally, provided that the narrow beam transmissions of theadditional RS, e.g. CSI-RS, are still available, the wireless device 10may perform a new narrow beam selection instead of a wide beam selectionand transmit the second (or third) preamble in accordance with the RACHconfiguration associated with the newly selected narrow beam.

Embodiments herein enable the wireless device 10 and the second radionetwork node 13 to identify potential error cases when narrow beamselection is performed combined with a handover and/or a transition frominactive to connected state based on a narrow DL beam and/or addition ofa connectivity leg to establish dual connectivity or multi-connectivityor to add a component carrier for carrier aggregation, and performfallback to the second beam such as a wide beam when some kind offailure in the RAR reception is detected. The advantage is mainly thatone may use e.g. the wide beams for static signals, use narrow beams fordynamic beamforming and, in the case of failures caused by the firste.g. narrow DL beam, the second radio network node 13 and the wirelessdevice 10 can fall back to the usage of the wide beams. Note that thenarrow beams used for transmission of additional RS may be temporarilytransmitted consecutively, i.e. beam swept and/or repeated during alimited time period, and during this limited time period the beams maybe transmitted with shorter intervals between the transmissions (evenback to back) than the intervals being used for the static signals.

Note that in a general scenario the term “radio network node” can besubstituted with “transmission point”. The key observation is that itmust be possible to make a distinction between the transmission points(TPs), typically based on MRSs or different synchronization signals andBRSs transmitted. Several TPs may be logically connected to the sameradio network node but if they are geographically separated, or arepointing in different propagation directions, the TPs will be subject tothe same mobility issues as different radio network nodes. In subsequentsections, the terms “radio network node” and “TP” can be thought of asinterchangeable.

The method actions performed by the wireless device 10 for handlingcommunication in the wireless communication network 1 according toembodiments herein will now be described with reference to a flowchartdepicted in FIG. 7a . The actions do not have to be taken in the orderstated below, but may be taken in any suitable order. Actions performedin some embodiments are marked with dashed boxes.

Action 701. The wireless device 10 may acquire synchronization with acell of the selected DL beam and may detect and select a second beam,e.g. a wider beam, using the acquired synchronization.

Action 702. The wireless device transmits to a radio network node, suchas the second radio network node 13 during e.g. a handover or the firstradio network node 12, a first preamble associated with a selected DLbeam. The DL beam may be selected based on signal strength or signalquality. This may be triggered by receiving a message indicating a cellselection or a handover.

Action 703. The wireless device 10 monitors for a RAR in a first RARreception window.

Action 704. When the RAR is not received in the first RAR receptionwindow, the wireless device 10 monitors for the RAR in a second RARreception window of a different beam. The second RAR reception windowmay be an extension of the first RAR reception window. The differentbeam may be a wider beam than the selected downlink beam; wider hereinmeaning covering a larger area than the selected DL beam.

Action 705. Alternatively, when the RAR is not received in the first RARreception window, the wireless device 10 transmits, to the second radionetwork node, the second preamble associated with the second beamwherein the first preamble is associated with a channel stateinformation reference signal and the second preamble is associated witha synchronization signal block.

Furthermore, when not receiving the RAR in the second RAR receptionwindow, the wireless device 10 may transmit the second preambleassociated with the second beam.

Action 706. When a RAR associated with the second preamble is notreceived, the wireless device 10 may transmit a third preamble of anewly selected beam.

The method actions performed by the radio network node e.g. the secondradio network node 13 but may also be the first radio network node 12for handling communication of the wireless device in the wirelesscommunication network 1 according to embodiments herein will now bedescribed with reference to a flowchart depicted in FIG. 7b . Theactions do not have to be taken in the order stated below, but may betaken in any suitable order. Actions performed in some embodiments aremarked with dashed boxes.

Action 711. The second radio network node 13 receives the first preambleassociated with the DL beam.

Action 712. The second radio network node 13 transmits the RAR, usingthe DL beam associated with the first preamble.

Action 713. The second radio network node 13 detects whether thewireless device has successfully received the RAR or not. E.g. thesecond radio network node 12 may fail to receive a subsequent messagerelated to the RAR from the wireless device 10.

Action 714. The second radio network node 13 sends the RAR a second timeusing a different beam when detected that the wireless device 10 has notsuccessfully received the RAR. The different beam covers the DL beam thewireless device 10 has initially selected. E.g. a center direction ofthe different beam is equal to a center direction of the selected DLbeam in action 702.

FIG. 7c is a combined flowchart and signaling scheme according toembodiments herein. The actions may be performed in any suitable order.

For example, the second radio network node 13 transmits its beams, i.e.the second radio network node 13 transmits reference signals (RS)associated with a respective beam, e.g. PSS, SSS, TSS, DMRS, CSI-RS,BRS, or similar.

Action 721. The wireless device 10 may perform repeatedly measurementson the reference signals, i.e. on a number of beams, transmitted fromthe second radio network node 13, over a set time interval.

Action 722. The first radio network node 12 may then receive ameasurement report and determine to request a handover for the wirelessdevice 10 (or a set of wireless devices) to a specific candidate targetservice area associated to the second radio network node 13. The firstradio network node 12 may then transmit, to the wireless device 10, ahandover command or a message indicating a handover of the wirelessdevice 10 to the second radio network node 13.

Action 723. The wireless device 10 selects beam and transmits apreamble, i.e. the first preamble, in accordance with the RACHconfiguration associated with the selected (best) narrow CSI-RS DL beam.

Action 724. The wireless device 10 then waits for a RAR in the regular(configured) RAR reception window, in which the network, in case ofsuccessful reception of the preamble, will use narrow beamforming totransmit the RAR. If the RAR is received, none of the herein considerederror cases will occur and the wireless device 10 proceeds with thenetwork access procedure.

Action 725. However, if the wireless device 10 does not receive any RARin the first RAR reception window, it instead waits for a RAR in thesecond reception window, in which the network, in case of failure toreceive a subsequent message, i.e. a message transmitted by the wirelessdevice 10 after receiving the RAR, transmits a RAR using a wide(r) beam.Note that this second RAR reception window may also be realized as anextension of the first RAR reception window, essentially forming asingle RAR reception window. If the wireless device 10 successfullyreceives a RAR in the second (or extended part of the) reception window,the wireless device 10 proceeds with the network access procedure.Alternatively, (not shown) when the RAR is not received in the first RARreception window, the wireless device 10 may transmit the secondpreamble associated with the second beam wherein the first preamble isassociated with a channel state information reference signal and thesecond preamble is associated with a synchronization signal block.

Action 726. However, if the wireless device 10 does not receive any RARin the second (or extended part of the) RAR reception window, thewireless device 10 transmits the second preamble such as a second RACHpreamble, this time associated with a wide beam. When doing this, thewireless device 10 uses the RACH configuration associated with a widebeam which either has been detected (and selected) previously, e.g. awide beam SS Block transmission which the wireless device 10 detectedwhen it acquired synchronization in the cell, or which the wirelessdevice 10 identifies during a new wide beam selection procedure. Thesetwo alternatives may also complement each other, such that a second RACHpreamble is transmitted based on the RACH configuration associated witha previously detected, and selected, wide beam, but if no RAR isreceived in response, then the wireless device 10 performs a new widebeam selection and transmits a third preamble in accordance with theRACH configuration of the newly selected wide beam.

Action 727. The second radio network node may transmit a RAR that isreceived at the wireless device.

Action 728. The second radio network node 13 and the wireless device 10may then communicate over a User Plane (UP) transmission.

Examples of actions performed by the wireless device 10 for handlingcommunication, such as enabling handover, of the wireless device 10 inthe communication network 1 according to some embodiments will now bedescribed with reference to a flowchart depicted in FIG. 8. The actionsdo not have to be taken in the order stated below, but may be taken inany suitable order. Actions performed in some embodiments are markedwith dashed boxes. Additional RSs are exemplified herein as CSI-RSs.

The wireless device 10 is configured to access a target cell (forexample during a handover execution procedure or during a transitionfrom inactive to connected state) with two mappings between DL beams andRACH resources:

-   -   A first mapping of RSs and RACH resources also referred to as a        narrow beam RACH configuration mapping (including multiple        narrow beams, e.g. identified by CSI-RS, and multiple        corresponding RACH configurations); and    -   A second mapping of RSs and RACH resources also referred to as a        wide beam RACH configuration mapping (fallback) (including one        or more wide beam(s), e.g. identified by TSS, and one or more        corresponding RACH configurations).

The wireless device 10 may receive (action 801) the two mappings, whichmay also be referred to as RACH mapping configurations. Upon receivingthose two mappings, the wireless device 10 may perform a selection of abest, based on e.g. signal strength or quality, DL narrow beam e.g.using the configured CSI-RS(s) in the target cell. The CSI-RS may bemapped to one of the received RACH mapping configurations, e.g.time/frequency resources, in order to transmit an allocated dedicatedpreamble.

The wireless device 10 may then transmit (action 802) a RACH preamblefrom a mapping such as the first mapping.

Upon transmitting the dedicated preamble, the wireless device 10 startsto monitor (action 803) the first RAR reception window such as a firstRandom Access Response (RAR) time window, which may also be configuredby the source cell, wherein the first radio network node 12, e.g. gNB,serving the source cell in turn may have received the RAR windowconfiguration from the second radio network node 13, e.g. gNB, servingthe target cell, e.g. during a handover preparation procedure.

If the wireless device 10 receives a RAR within that configured firstRAR reception window, the wireless device 10 continues the random accessprocedure and, using the UL grant received in the RAR the wirelessdevice 10 transmits (action 804) the HO complete message (or the message3 associated with the establishment of dual connectivity, carrieraggregation or even a transition from inactive to connected state). Thesuccessful reception of the RAR from the target radio network nodeindicates to the wireless device 10 that the target cell hassuccessfully detected the preamble and consequently the association withthe best narrow DL beam covering the wireless device 10.

According to embodiments herein, if the wireless device 10 does notreceive a RAR within that configured RAR time window, the wirelessdevice 10 will trigger (action 805) the second RAR time window (noticethat embodiments herein also apply using a single longer RAR timewindow), which is part of e.g. the wide beam mapping configuration.Optionally the wireless device 10 adapts its receive beam (if used) to awider configuration matching the wider beam the network will use for thesecond RAR transmission attempt. If the wireless device 10 receives theRAR within that second RAR time window the wireless device 10 maycontinue the random access procedure and may transmit (action 806) theHO complete message (or the message 3 associated with the establishmentof dual connectivity, carrier aggregation or a transition from inactiveto connected state). The successful reception of the RAR from the targetin the second window (or in the second part of the long single RAR timewindow) indicates to the wireless device 10 that the radio network nodehas successfully detected e.g. the preamble associated with a narrow DLbeam that was the best at the moment when the wireless device 10selected the beam but it has changed when the network transmitted thefirst RAR attempt (to the point it could not be detected, i.e. thewireless device 10 had moved out of the coverage of the selected narrowDL beam). In other words, receiving the RAR in the second part of thewindow (or in the second RAR window) indicates that change.

If the wireless device 10 does not receive a RAR within the second RARtime window, which may be part of the wide beam mapping configuration,the wireless device 10 may perform a wide beam selection (action 807)i.e. select the best wide beam of the target cell. That selection may bedone, for example, by performing measurements on a SS Burst Set andusing e.g. the TSS to make a distinction among wide beams in the SSBlock Burst. Note that the wireless device 10 might have been performingthese measurements even trying to access the target cell, in some kindof wide beam tracking so that processes could be speeded up.

The outcome of the wide DL beam selection may be a TSS (or any otherwide beam indication) that can be mapped to one of the received widebeam RACH configurations at the wireless device 10, received from thesource cell. After the wide DL beam selection, the wireless device 10may transmit the configured preamble in the RACH resource associatedwith the mapped configuration. After transmitting the preamble, thewireless device 10 may wait (action 808) for a third (fallback) RAR timewindow. If the wireless device 10 receives the RAR within the third RARtime window the wireless device 10 may continue the random accessprocedure and transmits (action 809) the HO complete message (or themessage 3 associated with the establishment of dual connectivity,carrier aggregation or even a transition from inactive to connectedstate). The successful reception of the RAR in the third time windowindicates to the wireless device that the radio network nodesuccessfully detected the second preamble transmission (that could bethe same preamble or not, depending on how the RACH configurationallocated preamble for the CSI-RS based procedures compared to thefallback procedure), associated with e.g. a wide DL beam that is not thesame that covered the initially best selected narrow CSI-RS beam. If thewireless device 10 cannot detect a RAR within that third time window,the wireless device 10 may perform power ramping procedures (action 810)as indicated in the system information and/or received as part of thesystem information and/or via the dedicated message as part of thefallback configuration.

An example realization of this fallback procedure is illustrated througha flowchart in FIG. 8.

A further aspect that may contribute to facilitating or speeding up theabove described fallback procedure, in particular the action involvingthe selection of the new beam exemplified as a wide beam selection andtransmission of the second preamble, see action 705, is that beforemeasuring on the CSI-RS, the wireless device 10 may acquiresynchronization, see action 701, in the concerned cell, unless theconcerned cell is tightly synchronized with another cell in which thewireless device 10 already has acquired synchronization, where “tightlysynchronized” means that the wireless device 10 should be able toreceive a DL transmission in one of the cells more or less within acyclic prefix when applying the synchronization of the other cell, e.g.a serving/source cell. The statement that the wireless device 10 may besynchronized with the target cell within the cyclic prefix to receivethe additional RS (e.g. CSI-RS) is based on the assumption that theadditional RS will not contain a synchronization component withproperties that allow the wireless device 10 to detect the RS bysearching through a large number of timing (and frequency) hypothesiswith a reasonable processing effort. The existence of suchsynchronization component in the additional RS is however notunconceivable, but more likely is that the additional RS will consist ofa signal with properties that make it good for channel qualitymeasurement purposes and allows the wireless device 10 to maintain finesynchronization. This is provided that the initial, coarsersynchronization within the cyclic prefix has already been achieved. Whenacquiring this synchronization in the concerned cell the wireless device10 receives the PSS, SSS and possibly TSS (which are part of the SSBlock transmissions) of the concerned cell. Having done this detectionof the SS Block transmission in the concerned cell, the wireless device10 may know in which resources to look for such transmissions during thefallback procedure. It is even possible that the wireless device 10 canconsider previously performed detections (and measurements) on SS Blocktransmissions as a proactively performed wide beam selection for thefallback procedure and assume that the RACH configuration associatedwith the “proactively” selected best wide beam as valid. The wirelessdevice 10 may then use this proactive wide beam selection andcorresponding RACH configuration to transmit the second preamble. Thiscould optionally be an intermediate action and if that also fails, thewireless device 10 performs the above described wide beam selection andtransmits a third preamble accordingly associated with the newlyselected beam in action 706. In order not to unnecessarily delay theoverall access procedure by using this intermediate step, the wirelessdevice 10 may initiate and perform the new wide beam selection inparallel, e.g. while waiting for a RAR in response to the preambletransmitted based on the RACH configuration associated with thepreviously selected wide beam.

An alternative to basing the fallback procedure on wide beam selectionmay be that the wireless device 10 restarts its narrow beam selectionbased on the narrow beam RS transmissions (e.g. CSI-RS transmissions).To enable this alternative, the additional RS may be configured to betransmitted over this extended period of time so that the wirelessdevice 10 has time to perform the narrow beam selection a second time.This CSI-RS configuration may be conditional, such that it is extendedin time only if the first RACH procedure (including the narrow beam RARand wide beam RAR) fails.

The wireless device 10 may receive a second RAR after receiving a firstRAR, for example, if the network erroneously determines that thewireless device 10 has not detected the first RAR (because thesubsequent message, e.g. Msg3 or handover complete message, was lost)and sends a second one. In that case the wireless device 10 may discardthe first RAR and proceed with the access procedure in accordance withthe second RAR.

Embodiments herein also comprise a radio Self-Organizing Network (SON)function where the wireless device 10 may store the failure relatedinformation to be possibly transmitted together with message 3 (or asfailure reports, e.g. on request from the radio network node). Thatcould comprise the radio conditions of the K best narrow DL beams thatgenerated the failure and/or the occurrence of a fallback procedure.That can enable the network to later optimize the procedure andeventually not transmit that anymore. That information can be providedto the source cell.

Note that nothing has been described in terms of wireless devicereceiver beamforming in these two different periods. The assumption isthat the wireless device 10 uses a wide RX beamforming for RAR detectionand/or the strongest RX beam previously selected during the beamselection procedure. Similarly, the wireless device 10 may also use thestrongest TX beam previously selection e.g. during some neighbor celltracking procedure or use a wide (even omnidirectional) TX beam or asweep of narrow beams, in case the RACH configuration is adapted towireless device TX beam sweeping.

During handover preparation a target node, such as the second radionetwork node 13, may provide a source node, such as the first radionetwork node 12, with two RACH configurations so the wireless device 10can access a target cell, wherein these RACH configurations arerespectively associated e.g. mapped with e.g. narrow DL beamtransmissions and wide DL beam transmissions, as described above. In thecase the procedure is to be used for the transition from RRC_INACTIVE toRRC_CONNECTED state the nodes reserving these resources could exchangethis information and define a validity time and/or area for theseresources. A possible alternative may also be to use common defaultconfigurations and their mappings to beams, which are known by allconcerned nodes, e.g. gNBs, in the network. Such default configurationsand mappings may be standardized and/or chosen by an operator andconfigured in all concerned nodes, e.g. gNBs, in the wirelesscommunication network.

Once this preparation phase between nodes is concluded, for example, thehandover preparation over the inter-node interface, e.g. betweendifferent nodes such as Xn in the case of NR, which can be acrossdifferent gNBs and/or even across different RATs. Note that in somecases such an inter-node interface may not be available and then thisinter-node communication can instead be relayed via one or more corenetwork nodes. The target node such as the second radio network node 13may monitor the PRACH resources associated with the different CSI-RSi.e. the target cell expects an incoming wireless device at certainPRACH resources where detection of the expected wireless device could bedone via the allocated preamble for contention-free random access.

If the configured preamble (or one of the configured preambles, in thecase the wireless device 10 has received dedicated preambles per CSI-RS)associated with narrow DL beam transmissions is detected at themonitored PRACH resources, the second radio network node 13 may preparea RAR and transmits it with the narrow DL beam associated with the PRACHdetection. After the transmission, the network, such as the second radionetwork node 13, monitors whether the wireless device 10 hassuccessfully received the RAR by the reception of the handover completemessage (or other message, e.g. in case of RRC_INACTIVE to RRC_CONNECTEDstate transition or addition of a connectivity leg to establish dualconnectivity or multi-connectivity and adding a component carrier forcarrier aggregation).

If the second radio network node 13 detects that the wireless device 10has successfully transmitted the handover complete message (or othermessage implying that the wireless device 10 successfully received theRAR), the procedure ends it since that is an indication that thewireless device 10 has received and decoded the RAR and that the accessprocedure is successfully completed.

If the network, e.g. the second radio network node 13, determines thatthe wireless device 10 may not have been able to decode the RAR, forexample, by the fact that it has not received the handover completemessage (or other message as described above) in the expected resources(scheduled by an UL grant in the transmitted RAR), the second radionetwork node 13 sends the RAR a second time but over a wide beam. Thewide DL beam that is selected by the second radio network node 13 shouldbe covering, i.e. overlapping, the narrow DL beam the wireless device 10has initially selected. The knowledge about which wide DL wide beam touse is obtained by checking the detected preamble (and the PRACHresources it was received in) to assume the previously detected narrowDL beam the wireless device 10 was detecting and choosing a wide beamthat covers the narrow beam, e.g. with the center direction of thesecond beam being equal to—or close to—the center direction of theselected DL (first) beam. It is also possible that a certain group ofnarrow beams may be associated with a certain wide beam, in which casethis wide beam would be used irrespective of which of the narrow beamsin the associated group of narrow beams the detected preamble wasassociated with, i.e. this may result in that the center direction ofthe narrow beam is located closer to a side edge of the wide beam thanto the center direction of the wide beam. As previously described, incase multiple narrow beams (e.g. CSI-RS transmissions) are associatedwith the same PRACH resources, their associated RACH configurations mayinstead differ in which preamble the wireless device 10 is to use.Hence, via the used PRACH resources and/or the preamble (transmitted bythe wireless device 10 and received by the second radio network node13), the second radio network node 13, e.g. gNB, may determine whichnarrow beam the wireless device 10 had selected as the best (even if itmay no longer be the best, which may be the reason the first RARtransmission failed) and based on that select an appropriate wide(second) beam.

-   -   If in the second attempt the second radio network node 13        detects that the wireless device 10 has successfully transmitted        the handover complete message in response to the second RAR, the        access procedure has successfully concluded and ends.    -   If in the second attempt to transmit the RAR the second radio        network node 13 detects that the wireless device 10 has not been        able to successfully decode the RAR, for example, by detecting        that no handover complete message (or other message) was        received in the UL resources allocated by the UL grant in the        second RAR, the second radio network node 13 may monitor its        PRACH resources associated with wide beam transmissions, such as        based on the TSS according to the configuration provided to the        wireless device 10.        -   As an option, the second radio network node 13, may take            additional proactive actions to avoid that the wireless            device 10 proceeds to transmit the second preamble. This            option can be used if there is some time left of the RAR            window when the UL transmission resources allocated by the            UL grant in the RAR has occurred. If so, and if no handover            complete message (or other message) was received in the UL            resources allocated by the UL grant in the RAR, the second            radio network node 13, may perform a DL wide beam sweeping            of the RAR and/or transmit the RAR in an even wider beam            until the second radio network node 13 detects the handover            complete message.

Another aspect on the network side relates to RACH resource partitioningfor narrow DL beam and wide DL beam access. Upon configuring thewireless device 10 via the source cell i.e. the first radio network node12, the target cell may select preamble per CSI-RS that enables thetarget cell to distinguish the DL narrow beams (e.g. in the case thesame time/frequency resources for PRACH are allocated per groups ofCSI-RSs) and, if relevant, the specific wireless device 10 (in the caseof contention-free random access). In one embodiment that distinction isenable by providing the same time/frequency resources for PRACH for aset of detectable CSI-RS and a distinct preamble per CSI-RS, e.g. uniquewithin the set of CSI-RS or unique among all CSI-RS in the cell, perconfigured incoming wireless device 10 so the network is able todistinguish between different wireless devices and DL beams to transmitthe RAR and later the subsequent transmissions, e.g. user planetransmissions and/or further control signaling, after the HO completemessage, or other message, depending on the type of access procedurebeing performed, as previously described.

If that also fails, the wireless device 10 is allowed to try to performanother measurement to update the strongest beam as long as theadditional RS (e.g. CSI-RS) are still being transmitted, e.g. it isstill within the configured time e.g. N subframes, i.e. a time periodwithin which the CSI-RS are transmitted and/or within which theirassociated RACH configurations are valid. If the wireless device 10 getsthe RAR but with low power, it means it could try to perform some powerramping method such as change the TX beamforming, e.g. use a narrower TXbeam with higher beam gain and/or increase the transmission power.

If the CSI-RSs, or other additional RS, are no longer available, ortheir associated RACH configurations are no longer valid, the wirelessdevice 10 may either use the tracking information about a best SS Blockbeam and use the previously configured RACH information per TSS or SSblock, more stable in terms of RACH procedure since the SS Block istransmitted in a wide beam. As previously mentioned, this may be basedon previous detection(s) of SS Block transmission(s) and/or on newdetection(s) of SS Block transmission(s) (to ensure fresh, up to datewide beam selection). In other words, that may be a last step thewireless device 10 tries to access the cell.

As a possible alternative embodiment, which in some cases may be fasterthan the procedure described above, the wireless device 10 and the radionetwork node could act as follows (described in relation to the abovedescription).

The wide beam transmission of the second RAR is skipped and the wirelessdevice 10, upon failure to receive the first RAR, goes directly to thefallback step of transmitting the second preamble. If speed highlyvalued, the wireless device 10 may use the RACH configuration associatedwith a previously selected wide beam (e.g. a SS Block transmissiondetected when the wireless device acquired synchronization in the cell).Otherwise, or in case no RAR is received in response to a preambletransmitted based on the RACH configuration associated with thepreviously selected wide beam, the wireless device 10 may initiate widebeam selection or, if the narrow beam transmissions of the additional RS(e.g. CSI-RS) are still available, narrow beam selection and transmit apreamble in accordance with the RACH configuration of the selected (wideor narrow) beam.

Embodiments herein may relate to the use of a wide DL beam configurationas a fallback in the case the second radio network node 13 fails to sendor the wireless device 10 fails to receive the RAR via the narrow DLbeam, configured via CSI-RS.

FIG. 9 is a block diagram depicting the wireless device 10, in twoembodiments, for handling communication of the wireless device in thewireless communication network 1 according to embodiments herein.

The wireless device 10 may comprise processing circuitry 901, e.g. oneor more processors, configured to perform the methods herein.

The wireless device may comprise a configuring module 902. The wirelessdevice 10, the processing circuitry 901, and/or the configuring module902 may be configured to access a target cell, the second service area14, (for example during a handover execution procedure or during atransition from RRC_INACTIVE to RRC_CONNECTED state) with two mappingsbetween DL beams and per cell RACH resources: i) a narrow beam RACHmapping to be initially used to access the target cell so that targetcan directly know the best DL narrow beam with which to send the RAR tothe wireless device 10 and start subsequent data transmission and ii) awide beam RACH mapping (fallback), to be used in the case the wirelessdevice 10 and network detects that the first procedure has failed. Thewireless device 10, the processing circuitry 901, and/or the configuringmodule 902 may be configured to acquire synchronization with a cell ofthe selected downlink beam; and to detect and select the second beamusing the acquired synchronization.

The wireless device may comprise a transmitting module 903, e.g. atransmitter or a transceiver. The wireless device 10, the processingcircuitry 901, and/or the transmitting module 903 is configured totransmit, to the radio network node 13, the first preamble associatedwith the selected downlink beam, e.g. transmit the first preamble inaccordance with the RACH configuration associated with the selected(best) narrow CSI-RS DL beam.

The wireless device may comprise a receiving module 904, e.g. a receiveror transceiver. The wireless device 10, the processing circuitry 901,and/or the receiving module 904 is configured to monitor for a RAR in afirst RAR reception window, e.g. wait for a RAR in the regular(configured) RAR reception window, in which the network, in case ofsuccessful reception of the preamble, will use narrow beamforming totransmit the RAR. If the RAR is received, none of the herein considerederror cases has occurred and the wireless device 10 proceeds with thenetwork access procedure. The wireless device 10, the processingcircuitry 901, and/or the transmitting module 903 may be configured to,when the RAR is not received in the first RAR reception window,transmit, to the radio network node, the second preamble associated withthe second beam wherein the first preamble is associated with a channelstate information reference signal and the second preamble is associatedwith a synchronization signal block.

The wireless device 10, the processing circuitry 901, and/or thereceiving module 904 may be configured to, when the RAR is not receivedin the first RAR reception window, monitor for the RAR in a second RARreception window of a different beam. The second RAR reception windowmay be an extension of the first RAR reception window. The differentbeam may be a wider beam than the selected downlink beam.

E.g., if the wireless device 10, the processing circuitry 901, and/orthe receiving module 904 does not receive any RAR in the regular RARreception window, the wireless device 10, the processing circuitry 901,and/or the receiving module 904 is further configured to wait for a RARin a second RAR reception window, in which the network such as thesecond radio network node 13, in case of failure to receive asubsequent, i.e. a message transmitted by the wireless device 10 afterreceiving the RAR, transmits a RAR using a wide(r) beam. Note that thissecond RAR reception window may also be realized as an extension of theregular RAR reception window, essentially forming a single RAR receptionwindow. If the wireless device 10, the processing circuitry 901, and/orthe receiving module 904 successfully receives a RAR in the second (orextended part of the) RAR reception window, the wireless device 10proceeds with the network access procedure.

The wireless device 10, the processing circuitry 901, and/or thereceiving module 904 may be configured to, when not receiving the RAR inin the second RAR reception window, transmit the second preambleassociated with a second beam; and when a RAR associated with the secondpreamble is not received, the wireless device 10, the processingcircuitry 901, and/or the transmitting module 903 may be configured totransmit the third preamble of a newly selected beam. E.g. if thewireless device 10, the processing circuitry 901, and/or the receivingmodule 904 does not receive any RAR in the second (or extended part ofthe) RAR reception window, the wireless device 10, the processingcircuitry 901, and/or the transmitting module 903 is configured totransmit a second RACH preamble, this time associated with a wide beam.When doing this, the wireless device 10, the processing circuitry 901,and/or the transmitting module 903 is configured to use the RACHconfiguration associated with a wide beam which either has been detected(and selected) previously, e.g. a wide beam SS Block transmission whichthe wireless device 10 detected when it acquired synchronization in thecell, or which the wireless device 10 identifies during a new wide beamselection procedure. These two alternatives may also complement eachother, such that a second RACH preamble is transmitted based on the RACHconfiguration associated with a previously detected, and selected, widebeam, but if no RAR is received in response, then the wireless device 10performs a new wide beam selection and transmits a third preamble inaccordance with the RACH configuration of the newly selected wide beam.

The wireless device 10 further comprises a memory 905. The memorycomprises one or more units to be used to store data on, such as RSs,strengths or qualities, RAR reception windows, RACH information,preambles, commands, applications to perform the methods disclosedherein when being executed, and similar.

The methods according to the embodiments described herein for thewireless device 10 are respectively implemented by means of e.g. acomputer program product 906 such as a computer program, comprisinginstructions, i.e., software code portions, which, when executed on atleast one processor, cause the at least one processor to carry out theactions described herein, as performed by the wireless device 10. Thecomputer program product 906 may be stored on a computer-readablestorage medium 907, e.g. a universal serial bus (USB) stick, a disc orsimilar. The computer-readable storage medium 907, having stored thereonthe computer program product, may comprise the instructions which, whenexecuted on at least one processor, cause the at least one processor tocarry out the actions described herein, as performed by the wirelessdevice 10. In some embodiments, the computer-readable storage medium maybe a non-transitory computer-readable storage medium. Thus, the wirelessdevice 10 may comprise the processing circuitry and the memory, saidmemory comprising instructions executable by said processing circuitrywhereby said wireless device is operative to perform the methods herein.

FIG. 10 is a block diagram depicting the second radio network node 13,in two embodiments, for handling communication of the wireless device inthe wireless communication network 1 according to embodiments herein.

The second radio network node 13 may comprise processing circuitry 1001,e.g. one or more processors, configured to perform the methods herein.

The second radio network node 13 may comprise a receiving module 1002,e.g. a receiver or a transceiver. The second radio network node 13, theprocessing circuitry 1001, and/or the receiving module 1002 isconfigured to receive the first preamble associated with the DL beamsuch as a first RACH preamble, from the wireless device 10.

The second radio network node 13 may comprise a transmitting module1003, e.g. a transmitter or a transceiver. The second radio network node13, the processing circuitry 1001, and/or the transmitting module 1003is configured to transmit the RAR using the DL beam associated with thefirst preamble. E.g. the second radio network node 13, the processingcircuitry 1001, and/or the transmitting module 1003 may be configured totransmit a first RAR to the wireless device 10. The second radio networknode 13, the processing circuitry 1001, and/or the receiving module 1002is configured to detect whether the wireless device 10 has successfullyreceived the RAR or not. The second radio network node 13, theprocessing circuitry 1001, and/or the receiving module 1002 may beconfigured to detect whether the wireless device 10 has successfullyreceived the RAR by failing to receive a subsequent message related tothe RAR from the wireless device 10.

The second radio network node 13, the processing circuitry 1001, and/orthe transmitting module 1003 is configured to send the RAR a second timeusing a different beam when detected that the wireless device 10 has notsuccessfully received the RAR, wherein the different beam covers the DLbeam the wireless device has initially selected.

E.g. the second radio network node 13, the processing circuitry 1001,and/or the transmitting module 1003 may be configured to determine thatthe wireless device 10 may not have been able to decode the RAR, forexample, by the fact that it has not received the handover completemessage (or other message as described above) in the expected resources(scheduled by an UL grant in the transmitted RAR), the second radionetwork node 13, the processing circuitry 1001, and/or the transmittingmodule 1003 sends the RAR a second time but over a wide beam. If in thesecond attempt to transmit the RAR the second radio network node 13, theprocessing circuitry 1001, and/or the transmitting module 1003 may beconfigured to detect that the wireless device 10 has not been able tosuccessfully decode the RAR, for example, by detecting that no handovercomplete message (or other message) was received in the UL resourcesallocated by the UL grant in the second RAR, the second radio networknode 13, the processing circuitry 1001, and/or the receiving module 1002may be configured to monitor its PRACH resources associated with widebeam transmissions, such as based on the TSS according to theconfiguration provided to the wireless device 10.

The second radio network node 13 further comprises a memory 1004. Thememory comprises one or more units to be used to store data on, such asRSs, strengths or qualities, RAR reception windows, RACH information,preambles, commands, applications to perform the methods disclosedherein when being executed, and similar.

The methods according to the embodiments described herein for the secondradio network node 13 are respectively implemented by means of e.g. acomputer program product 1005 e.g. a computer program, comprisinginstructions, i.e., software code portions, which, when executed on atleast one processor, cause the at least one processor to carry out theactions described herein, as performed by the second radio network node13. The computer program product 1005 may be stored on acomputer-readable storage medium 1006, e.g. a USB stick, a disc orsimilar. The computer-readable storage medium 1006, having storedthereon the computer program product, may comprise the instructionswhich, when executed on at least one processor, cause the at least oneprocessor to carry out the actions described herein, as performed by thesecond radio network node 13. In some embodiments, the computer-readablestorage medium may be a non-transitory computer-readable storage medium.Thus, the second radio network node 13 may comprise the processingcircuitry and the memory, said memory comprising instructions executableby said processing circuitry whereby said radio network node isoperative to perform the methods herein.

FIG. 11 is a block diagram depicting the first radio network node 12, intwo embodiments, for handling communication in the wirelesscommunication network 1 according to embodiments herein. The first radionetwork node 12 may be configured to serve the wireless device byproviding radio coverage over the first service area 11 or beam usingthe first reference signal for identifying the first service area 11 inthe wireless communication network 1. The second radio network node 13is configured to provide radio coverage over the second service area 14using the second reference signal for identifying the second servicearea 14 in the wireless communication network 1.

The first radio network node 12 may comprise a processing unit 1101,e.g. one or more processors, configured to perform the methods herein.

The first radio network node 12 may comprise a receiving module 1102.The first radio network node 12, the processing unit 1101, and/or thereceiving module 1102 is configured to receive configuration data fromthe second radio network node or a target cell.

The first radio network node 12 may comprise a transmitting module 1103.The first radio network node 12, the processing unit 1101, and/or thetransmitting module 1003 is configured to transmit the configurationdata to the wireless device informing the wireless device of RACHinformation of the beams of the second radio network node 13.

The first radio network node 12 further comprises a memory 1104. Thememory comprises one or more units to be used to store data on, such asRACH information, RAR windows, RSs, applications to perform the methodsdisclosed herein when being executed, and similar.

The methods according to the embodiments described herein for firstradio network node 12 are respectively implemented by means of e.g. acomputer program product 1105 e.g. a computer program, comprisinginstructions, i.e., software code portions, which, when executed on atleast one processor, cause the at least one processor to carry out theactions described herein, as performed by the first radio network node12. The computer program product 1105 may be stored on acomputer-readable storage medium 1106, e.g. a USB stick, a disc orsimilar. The computer-readable storage medium 1106, having storedthereon the computer program product, may comprise the instructionswhich, when executed on at least one processor, cause the at least oneprocessor to carry out the actions described herein, as performed by thefirst radio network node 12. In some embodiments, the computer-readablestorage medium may be a non-transitory computer-readable storage medium.Thus, the first radio network node 12 may comprise the processingcircuitry and the memory, said memory comprising instructions executableby said processing circuitry whereby said radio network node isoperative to perform the methods herein.

In some embodiments a more general term “radio network node” is used andit can correspond to any type of radio network node or any network node,which communicates with a wireless device and/or with another networknode. Examples of network nodes are NodeB, Master eNB, Secondary eNB, anetwork node belonging to Master cell group (MCG) or Secondary CellGroup (SCG), base station (BS), multi-standard radio (MSR) radio nodesuch as MSR BS, eNodeB, network controller, radio network controller(RNC), base station controller (BSC), relay, donor node controllingrelay, base transceiver station (BTS), access point (AP), transmissionpoints, transmission nodes, Remote Radio Unit (RRU), Remote Radio Head(RRH), nodes in distributed antenna system (DAS), core network node e.g.Mobility Switching Centre (MSC), Mobile Management Entity (MME) etc,Operation and Maintenance (O&M), Operation Support System (OSS),Self-Organizing Network (SON), positioning node e.g. Evolved ServingMobile Location Centre (E-SMLC), Minimizing Drive Test (MDT) etc.

In some embodiments the non-limiting term wireless device or userequipment (UE) is used and it refers to any type of wireless devicecommunicating with a network node and/or with another UE in a cellularor mobile communication system. Examples of UE are target device,device-to-device (D2D) UE, proximity capable UE (aka ProSe UE), machinetype UE or UE capable of machine to machine (M2M) communication, PDA,PAD, Tablet, mobile terminals, smart phone, laptop embedded equipped(LEE), laptop mounted equipment (LME), USB dongles etc.

The embodiments are described for 5G. However the embodiments areapplicable to any RAT or multi-RAT systems, where the UE receives and/ortransmit signals (e.g. data) e.g. LTE, LTE FDD/TDD, WCDMA/HSPA,GSM/GERAN, Wi Fi, WLAN, CDMA2000 etc.

Measurement Reference Signal (MRS): As used herein, a “MRS” is anysignal used for mobility measurements in Mobility measurement beams.Thus, while the term “MRS” is used herein to refer a signal used herein,the term “MRS” is to be construed broadly to mean any signal, regardlessof what the signal is named, e.g., in any particular standard, used formobility measurements and, in particular, used according to theembodiments described herein. In some embodiments, a MRS is a mobilityspecific signal that is used for handover/beam switching purposes. Thisreference signal can be periodic or aperiodic. It can be configured tobe wireless device specific or could be used common for more than onewireless device.

As will be readily understood by those familiar with communicationsdesign, that functions means or modules may be implemented using digitallogic and/or one or more microcontrollers, microprocessors, or otherdigital hardware. In some embodiments, several or all of the variousfunctions may be implemented together, such as in a singleapplication-specific integrated circuit (ASIC), or in two or moreseparate devices with appropriate hardware and/or software interfacesbetween them. Several of the functions may be implemented on a processorshared with other functional components of a wireless device or networknode, for example.

Alternatively, several of the functional elements of the processingmeans discussed may be provided through the use of dedicated hardware,while others are provided with hardware for executing software, inassociation with the appropriate software or firmware. Thus, the term“processor” or “controller” as used herein does not exclusively refer tohardware capable of executing software and may implicitly include,without limitation, digital signal processor (DSP) hardware, read-onlymemory (ROM) for storing software, random-access memory for storingsoftware and/or program or application data, and non-volatile memory.Other hardware, conventional and/or custom, may also be included.Designers of communications devices will appreciate the cost,performance, and maintenance tradeoffs inherent in these design choices.

With reference to FIG. 12, in accordance with an embodiment, acommunication system includes a telecommunication network 3210, such asa 3GPP-type cellular network, which comprises an access network 3211,such as a radio access network, and a core network 3214. The accessnetwork 3211 comprises a plurality of base stations 3212 a, 3212 b, 3212c, such as NBs, eNBs, gNBs or other types of wireless access pointsbeing examples of the radio network node 12 herein, each defining acorresponding coverage area 3213 a, 3213 b, 3213 c. Each base station3212 a, 3212 b, 3212 c is connectable to the core network 3214 over awired or wireless connection 3215. A first user equipment (UE) 3291,being an example of the wireless device 10, located in coverage area3213 c is configured to wirelessly connect to, or be paged by, thecorresponding base station 3212 c. A second UE 3292 in coverage area3213 a is wirelessly connectable to the corresponding base station 3212a. While a plurality of UEs 3291, 3292 are illustrated in this example,the disclosed embodiments are equally applicable to a situation where asole UE is in the coverage area or where a sole UE is connecting to thecorresponding base station 3212.

The telecommunication network 3210 is itself connected to a hostcomputer 3230, which may be embodied in the hardware and/or software ofa standalone server, a cloud-implemented server, a distributed server oras processing resources in a server farm. The host computer 3230 may beunder the ownership or control of a service provider, or may be operatedby the service provider or on behalf of the service provider. Theconnections 3221, 3222 between the telecommunication network 3210 andthe host computer 3230 may extend directly from the core network 3214 tothe host computer 3230 or may go via an optional intermediate network3220. The intermediate network 3220 may be one of, or a combination ofmore than one of, a public, private or hosted network; the intermediatenetwork 3220, if any, may be a backbone network or the Internet; inparticular, the intermediate network 3220 may comprise two or moresub-networks (not shown).

The communication system of FIG. 12 as a whole enables connectivitybetween one of the connected UEs 3291, 3292 and the host computer 3230.The connectivity may be described as an over-the-top (OTT) connection3250. The host computer 3230 and the connected UEs 3291, 3292 areconfigured to communicate data and/or signaling via the OTT connection3250, using the access network 3211, the core network 3214, anyintermediate network 3220 and possible further infrastructure (notshown) as intermediaries. The OTT connection 3250 may be transparent inthe sense that the participating communication devices through which theOTT connection 3250 passes are unaware of routing of uplink and downlinkcommunications. For example, a base station 3212 may not or need not beinformed about the past routing of an incoming downlink communicationwith data originating from a host computer 3230 to be forwarded (e.g.,handed over) to a connected UE 3291. Similarly, the base station 3212need not be aware of the future routing of an outgoing uplinkcommunication originating from the UE 3291 towards the host computer3230.

Example implementations, in accordance with an embodiment, of the UE,base station and host computer discussed in the preceding paragraphswill now be described with reference to FIG. 13. In a communicationsystem 3300, a host computer 3310 comprises hardware 3315 including acommunication interface 3316 configured to set up and maintain a wiredor wireless connection with an interface of a different communicationdevice of the communication system 3300. The host computer 3310 furthercomprises processing circuitry 3318, which may have storage and/orprocessing capabilities. In particular, the processing circuitry 3318may comprise one or more programmable processors, application-specificintegrated circuits, field programmable gate arrays or combinations ofthese (not shown) adapted to execute instructions. The host computer3310 further comprises software 3311, which is stored in or accessibleby the host computer 3310 and executable by the processing circuitry3318. The software 3311 includes a host application 3312. The hostapplication 3312 may be operable to provide a service to a remote user,such as a UE 3330 connecting via an OTT connection 3350 terminating atthe UE 3330 and the host computer 3310. In providing the service to theremote user, the host application 3312 may provide user data which istransmitted using the OTT connection 3350.

The communication system 3300 further includes a base station 3320provided in a telecommunication system and comprising hardware 3325enabling it to communicate with the host computer 3310 and with the UE3330. The hardware 3325 may include a communication interface 3326 forsetting up and maintaining a wired or wireless connection with aninterface of a different communication device of the communicationsystem 3300, as well as a radio interface 3327 for setting up andmaintaining at least a wireless connection 3370 with a UE 3330 locatedin a coverage area (not shown in FIG. 13) served by the base station3320. The communication interface 3326 may be configured to facilitate aconnection 3360 to the host computer 3310. The connection 3360 may bedirect or it may pass through a core network (not shown in FIG. 13) ofthe telecommunication system and/or through one or more intermediatenetworks outside the telecommunication system. In the embodiment shown,the hardware 3325 of the base station 3320 further includes processingcircuitry 3328, which may comprise one or more programmable processors,application-specific integrated circuits, field programmable gate arraysor combinations of these (not shown) adapted to execute instructions.The base station 3320 further has software 3321 stored internally oraccessible via an external connection.

The communication system 3300 further includes the UE 3330 alreadyreferred to. Its hardware 3335 may include a radio interface 3337configured to set up and maintain a wireless connection 3370 with a basestation serving a coverage area in which the UE 3330 is currentlylocated. The hardware 3335 of the UE 3330 further includes processingcircuitry 3338, which may comprise one or more programmable processors,application-specific integrated circuits, field programmable gate arraysor combinations of these (not shown) adapted to execute instructions.The UE 3330 further comprises software 3331, which is stored in oraccessible by the UE 3330 and executable by the processing circuitry3338. The software 3331 includes a client application 3332. The clientapplication 3332 may be operable to provide a service to a human ornon-human user via the UE 3330, with the support of the host computer3310. In the host computer 3310, an executing host application 3312 maycommunicate with the executing client application 3332 via the OTTconnection 3350 terminating at the UE 3330 and the host computer 3310.In providing the service to the user, the client application 3332 mayreceive request data from the host application 3312 and provide userdata in response to the request data. The OTT connection 3350 maytransfer both the request data and the user data. The client application3332 may interact with the user to generate the user data that itprovides.

It is noted that the host computer 3310, base station 3320 and UE 3330illustrated in FIG. 13 may be identical to the host computer 3230, oneof the base stations 3212 a, 3212 b, 3212 c and one of the UEs 3291,3292 of FIG. 12, respectively. This is to say, the inner workings ofthese entities may be as shown in FIG. 13 and independently, thesurrounding network topology may be that of FIG. 12.

In FIG. 13, the OTT connection 3350 has been drawn abstractly toillustrate the communication between the host computer 3310 and the userequipment 3330 via the base station 3320, without explicit reference toany intermediary devices and the precise routing of messages via thesedevices. Network infrastructure may determine the routing, which it maybe configured to hide from the UE 3330 or from the service provideroperating the host computer 3310, or both. While the OTT connection 3350is active, the network infrastructure may further take decisions bywhich it dynamically changes the routing (e.g., on the basis of loadbalancing consideration or reconfiguration of the network).

The wireless connection 3370 between the UE 3330 and the base station3320 is in accordance with the teachings of the embodiments describedthroughout this disclosure. One or more of the various embodimentsimprove the performance of OTT services provided to the UE 3330 usingthe OTT connection 3350, in which the wireless connection 3370 forms thelast segment. More precisely, the teachings of these embodiments mayimprove the latency since the second or different beam is quicklyaccessed and thereby provide benefits such as reduced user waiting time,and better responsiveness.

A measurement procedure may be provided for the purpose of monitoringdata rate, latency and other factors on which the one or moreembodiments improve. There may further be an optional networkfunctionality for reconfiguring the OTT connection 3350 between the hostcomputer 3310 and UE 3330, in response to variations in the measurementresults. The measurement procedure and/or the network functionality forreconfiguring the OTT connection 3350 may be implemented in the software3311 of the host computer 3310 or in the software 3331 of the UE 3330,or both. In embodiments, sensors (not shown) may be deployed in or inassociation with communication devices through which the OTT connection3350 passes; the sensors may participate in the measurement procedure bysupplying values of the monitored quantities exemplified above, orsupplying values of other physical quantities from which software 3311,3331 may compute or estimate the monitored quantities. The reconfiguringof the OTT connection 3350 may include message format, retransmissionsettings, preferred routing etc.; the reconfiguring need not affect thebase station 3320, and it may be unknown or imperceptible to the basestation 3320. Such procedures and functionalities may be known andpracticed in the art. In certain embodiments, measurements may involveproprietary UE signaling facilitating the host computer's 3310measurements of throughput, propagation times, latency and the like. Themeasurements may be implemented in that the software 3311, 3331 causesmessages to be transmitted, in particular empty or ‘dummy’ messages,using the OTT connection 3350 while it monitors propagation times,errors etc.

FIG. 14 is a flowchart illustrating a method implemented in acommunication system, in accordance with one embodiment. Thecommunication system includes a host computer, a base station and a UEwhich may be those described with reference to FIGS. 12 and 13. Forsimplicity of the present disclosure, only drawing references to FIG. 14will be included in this section. In a first step 3410 of the method,the host computer provides user data. In an optional substep 3411 of thefirst step 3410, the host computer provides the user data by executing ahost application. In a second step 3420, the host computer initiates atransmission carrying the user data to the UE. In an optional third step3430, the base station transmits to the UE the user data which wascarried in the transmission that the host computer initiated, inaccordance with the teachings of the embodiments described throughoutthis disclosure. In an optional fourth step 3440, the UE executes aclient application associated with the host application executed by thehost computer.

FIG. 15 is a flowchart illustrating a method implemented in acommunication system, in accordance with one embodiment. Thecommunication system includes a host computer, a base station and a UEwhich may be those described with reference to FIGS. 12 and 13. Forsimplicity of the present disclosure, only drawing references to FIG. 15will be included in this section. In a first step 3510 of the method,the host computer provides user data. In an optional substep (not shown)the host computer provides the user data by executing a hostapplication. In a second step 3520, the host computer initiates atransmission carrying the user data to the UE. The transmission may passvia the base station, in accordance with the teachings of theembodiments described throughout this disclosure. In an optional thirdstep 3530, the UE receives the user data carried in the transmission.

FIG. 16 is a flowchart illustrating a method implemented in acommunication system, in accordance with one embodiment. Thecommunication system includes a host computer, a base station and a UEwhich may be those described with reference to FIGS. 12 and 13. Forsimplicity of the present disclosure, only drawing references to FIG. 16will be included in this section. In an optional first step 3610 of themethod, the UE receives input data provided by the host computer.Additionally or alternatively, in an optional second step 3620, the UEprovides user data. In an optional substep 3621 of the second step 3620,the UE provides the user data by executing a client application. In afurther optional substep 3611 of the first step 3610, the UE executes aclient application which provides the user data in reaction to thereceived input data provided by the host computer. In providing the userdata, the executed client application may further consider user inputreceived from the user. Regardless of the specific manner in which theuser data was provided, the UE initiates, in an optional third substep3630, transmission of the user data to the host computer. In a fourthstep 3640 of the method, the host computer receives the user datatransmitted from the UE, in accordance with the teachings of theembodiments described throughout this disclosure.

FIG. 17 is a flowchart illustrating a method implemented in acommunication system, in accordance with one embodiment. Thecommunication system includes a host computer, a base station and a UEwhich may be those described with reference to FIGS. 12 and 13. Forsimplicity of the present disclosure, only drawing references to FIG. 17will be included in this section. In an optional first step 3710 of themethod, in accordance with the teachings of the embodiments describedthroughout this disclosure, the base station receives user data from theUE. In an optional second step 3720, the base station initiatestransmission of the received user data to the host computer. In a thirdstep 3730, the host computer receives the user data carried in thetransmission initiated by the base station.

It is herein disclosed a method performed by a wireless device forhandling communication such as handling handover, in a wirelesscommunication network. The wireless device is configured to transmit afirst preamble in accordance with a RACH configuration associated with aselected narrow DL beam. The wireless device waits for a RAR in a(configured) first RAR reception window. If the RAR is received thewireless device 10 proceeds with the network access procedure. In casethe RAR in the first RAR reception window is not received, the wirelessdevice, waits for a RAR in a second RAR reception window of a wide(r)beam. If the wireless device receives a RAR in the second RAR receptionwindow, the wireless device proceeds with the network access procedure.In case the wireless device does not receive any RAR in the second RARreception window, the wireless device may transmit a second RACHpreamble associated with a wide beam. In case no RAR is received afterthe second RACH preamble the wireless device may transmit a thirdpreamble in accordance with a RACH configuration of a newly selectedwide beam.

It is further herein disclosed a method performed by a radio networknode for handling communication of a wireless device in a wirelesscommunication network. The radio network node, e.g. a second radionetwork node, receives a first preamble associated with a narrow DL beamtransmission and transmits a RAR with the narrow DL beam associated withthe first preamble. The radio network node monitors whether the wirelessdevice has successfully received the RAR and determines that thewireless device 10 may not have been able to decode the RAR, the secondradio network node sends the RAR a second time but over a wide beam. Thewide DL beam that is selected by the second radio network node 13 coversthe narrow DL beam the wireless device has initially selected.

It will be appreciated that the foregoing description and theaccompanying drawings represent non-limiting examples of the methods andapparatus taught herein. As such, the apparatus and techniques taughtherein are not limited by the foregoing description and accompanyingdrawings. Instead, the embodiments herein are limited only by thefollowing claims and their legal equivalents.

ABBREVIATIONS

ACK Acknowledged

ADC Analog-to-digital conversion

AGC Automatic gain control

ANR Automatic neighbor relations

AP Access point

BCH Broadcast channel

BLER Block error rate

BRS Beam Reference Signal

BS Base station

BSC Base station controller

BTS Base transceiver station

CA Carrier aggregation

CC Component carrier

CG Cell group

CGI Cell global identity

CP Cyclic prefix

CPICH Common pilot channel

CQI Channel Quality Indicator

CSG Closed subscriber group

CSI-RS Channel State Information Reference Signal

DAS Distributed antenna system

DC Dual connectivity

DFT Discrete Fourier Transform

DL Downlink

DL-SCH Downlink shared channel

DRX Discontinuous reception

EARFCN Evolved absolute radio frequency channel number

ECGI Evolved CGI

eNB eNodeB

FDD Frequency division duplex

FFT Fast Fourier transform

HD-FDD Half duplex FDD

HO Handover

ID Identity

M2M machine to machine

MAC Media access control

MCG Master cell group

MDT Minimization of drive tests

MeNB Master eNode B

MIB Master information block

MME Mobility management entity

MRS Mobility Reference Signal

MRTD Maximum receive timing difference

MSR Multi-standard radio

NACK Not acknowledged

OFDM Orthogonal frequency-division multiplexing

RI Rank Indicator

SI System Information

PCC Primary component carrier

PCI Physical cell identity

PCell Primary Cell

PCG Primary Cell Group

PCH Paging channel

PDU Protocol data unit

PGW Packet gateway

PHICH Physical HARQ indication channel

PLMN Public land mobile network

PMI Precoding Matrix Indicator

PSCell Primary SCell

PSC Primary serving cell

PSS Primary synchronization signal

RAT Radio access Technology

RF Radio frequency

RLM Radio link monitoring

RNC Radio network Controller

RRC Radio resource control

RRH Remote radio head

RRU Remote radio unit

RSCP Received signal code power

RSRP Reference Signal Received Power

RSRQ Reference Signal Received Quality

RSSI Received signal strength indication

RSTD Reference signal time difference

RV Redundancy version

Rx Receiver

SCC Secondary component carrier

SCell Secondary Cell

SCG Secondary Cell Group

SeNB Secondary eNode B

SFN System frame number

SGW Signaling gateway

SI System information

SIB System information block

SIB1 System information block type 1

SINR Signal to interference and noise ratio

SON Self-organizing networks

SSC Secondary serving cell

SSS Secondary synchronization signal

TA Timing advance

TAG Timing advance group

TDD Time division duplex

Tx Transmitter

UARFCN UMTS Absolute Radio Frequency Channel Number

UE User equipment

UL Uplink

1. A method of operating a network node in a wireless communication network, the method comprising: receiving a first preamble associated with a first downlink (“DL”) beam from a wireless device in the wireless communication network; transmitting a random access response (“RAR”) to the wireless device using the first DL beam associated with the first preamble; and responsive to transmitting the RAR using the first DL beam, determining that the wireless device has not received the RAR; and responsive to determining that the wireless device has not received the RAR, transmitting the RAR using a second DL beam.
 2. The method of claim 1, wherein the second DL beam covers the first DL beam.
 3. The method of claim 1, further comprising: responsive to transmitting the RAR using the second DL beam, receiving a second preamble associated with a third DL beam from the wireless device, wherein the first preamble is associated with a channel state information reference signal and the second preamble is associated with a synchronization signal block.
 4. The method of claim 3, wherein the second DL beam and the third DL beam are wider than the first DL beam.
 5. The method of claim 3, wherein transmitting the RAR using the first DL beam comprises transmitting the RAR using the first DL beam during a first RAR reception window, the first DL beam having been selected by the wireless device, wherein transmitting the RAR using the second DL beam comprises transmitting the RAR using the second DL beam during a second RAR reception window, and wherein the second RAR reception window is an extension of the first RAR reception window.
 6. The method of claim 5, wherein determining that the wireless device has not received the RAR comprises determining that the network node has not received a subsequent message related to the RAR from the wireless device during a period of time associated with the first RAR reception window.
 7. The method of claim 5, wherein receiving the second preamble comprises, responsive to determining that the RAR has not been received during the second RAR reception window, receiving the second preamble associated with the third DL beam, the method further comprising: responsive to receiving the second preamble, transmitting a RAR associated with the second preamble during a third RAR reception window; determining that the wireless device has not received the RAR associated with the second preamble during the third RAR reception window; and responsive determining that the wireless device has not received the RAR associated with the second preamble during the third RAR reception window, receiving a third preamble of a fourth DL beam, the fourth DL beam having been selected by the wireless device.
 8. The method of claim 7, further comprising: responsive to a RAR associated with the third preamble not being received during a fourth RAR reception window, performing power ramping procedures based on system information.
 9. The method of claim 1, further comprising: transmitting a radio resource control (“RRC”) connection reconfiguration message including random access channel (“RACH”) mapping configuration to the wireless device, wherein the first DL beam and the second DL are associated with the RACH mapping configurations.
 10. A network node configured to operate in a wireless communication network, the network node comprising: processing circuitry; and memory coupled to the processing circuitry and having instructions stored therein that are executable by the processing circuitry to cause the network node to perform operations comprising: receiving a first preamble associated with a first downlink (“DL”) beam from a wireless device in the wireless communication network; transmitting a random access response (“RAR”) to the wireless device using the first DL beam associated with the first preamble; and responsive to transmitting the RAR using the first DL beam, determining that the wireless device has not received the RAR; and responsive to determining that the wireless device has not received the RAR, transmitting the RAR using a second DL beam.
 11. The network node of claim 10, wherein the second DL beam covers the first DL beam.
 12. The network node of claim 10, the operations further comprising: responsive to transmitting the RAR using the second DL beam, receiving a second preamble associated with a third DL beam from the wireless device, wherein the first preamble is associated with a channel state information reference signal and the second preamble is associated with a synchronization signal block.
 13. The network node of claim 12, wherein the second DL beam and the third DL beam are wider than the first DL beam.
 14. The network node of claim 12, wherein transmitting the RAR using the first DL beam comprises transmitting the RAR using the first DL beam during a first RAR reception window, the first DL beam having been selected by the wireless device, wherein transmitting the RAR using the second DL beam comprises transmitting the RAR using the second DL beam during a second RAR reception window, and wherein the second RAR reception window is an extension of the first RAR reception window.
 15. The network node of claim 14, wherein determining that the wireless device has not received the RAR comprises determining that the network node has not received a subsequent message related to the RAR from the wireless device during a period of time associated with the first RAR reception window.
 16. The network node of claim 14, wherein receiving the second preamble comprises, responsive to determining that the RAR has not been received during the second RAR reception window, receiving the second preamble associated with the third DL beam, the operations further comprising: responsive to receiving the second preamble, transmitting a RAR associated with the second preamble during a third RAR reception window; determining that the wireless device has not received the RAR associated with the second preamble during the third RAR reception window; and responsive determining that the wireless device has not received the RAR associated with the second preamble during the third RAR reception window, receiving a third preamble of a fourth DL beam, the fourth DL beam having been selected by the wireless device.
 17. The network node of claim 16, the operations further comprising: responsive to a RAR associated with the third preamble not being received during a fourth RAR reception window, performing power ramping procedures based on system information.
 18. The network node of claim 10, the operations further comprising: transmitting a radio resource control (“RRC”) connection reconfiguration message including random access channel (“RACH”) mapping configuration to the wireless device, wherein the first DL beam and the second DL are associated with the RACH mapping configurations.
 19. A non-transitory computer-readable medium having instructions stored therein that are executable by processing circuitry of a network node in a wireless communication network to cause the network node to perform operations, the operations comprising: receiving a first preamble associated with a first downlink (“DL”) beam from a wireless device in the wireless communication network; transmitting a random access response (“RAR”) to the wireless device using the first DL beam associated with the first preamble; and responsive to transmitting the RAR using the first DL beam, determining that the wireless device has not received the RAR; and responsive to determining that the wireless device has not received the RAR, transmitting the RAR using a second DL beam.
 20. The non-transitory computer-readable medium of claim 19, wherein the second DL beam covers the first DL beam. 